1. Field of the Invention
The present invention relates to a reciprocating power tool, such as a reciprocating saw, and more particularly, to a practical technique of reducing vibration in a reciprocating power tool with a simple structure, taking into account the behavior of the tool bit in actual operation of cutting a workpiece.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2001-9632 (D1) discloses a reciprocating saw. The known saw includes a motion converting mechanism for causing a slider to reciprocate via the rotational movement of the motor. A tool bit is mounted on the end of the slider. Further, a counter weight is provided in the motion converting mechanism. When the slider reciprocates, the counter weight reciprocates in a direction opposite to the reciprocating direction of the slider. As a result, vibration caused by reciprocating movement of the slider can be reduced.
By using such a counter weight that reciprocates with a 180° phase shift with respect to the reciprocating movement of the slider, the momentum mainly including the inertial force can be reduced between the slider and the counter weight in the axial direction of the slider. However, optimum timing for vibration reduction by the counter weight differs, according to the presence or absence of external resistance that acts on the tool bit, between the state in which the cutting operation is actually performed on the workpiece by the tool bit and the state in which the power tool is idled without performing a cutting operation. Further, even in the operation of cutting a workpiece, the external resistance that acts on the tool bit varies in a certain range according to various factors.